Connector pins for electric connection are known as structure for conductively connecting, via elastic contact, and providing signal transfer between electronic circuits on a pair of boards disposed opposite each other in a variety of electronic devices (see Japanese Patent Application Laid-open No. H7-161401). Furthermore, the inventor suggested pressure contact holding-type connectors with improved connector pins for electric connection (Japanese Patent Applications Laid-open No. 2002-100431, 2002-158052, and 2002-158053).
A connector pin for electric connection (Japanese Patent Application Laid-open No. H7-161401) is described, as shown in FIG. 10, as a connector 46 for electric connection, comprising: a connector pin 43 that is extendably and slidably fitted into a tubular body 41, locked inside thereof, and impelled in an extending direction by a spring 42 located inside the tubular body 41 and providing for electric conduction between the connector pin 43 and tubular body 41 via a sliding contact section of an outer peripheral surface 44 of a mating section of the connector pin 43 and an inner peripheral surface 45 of the tubular body 41 in a contracted state of the connector pin 43, wherein a small-diameter relief section 47 is provided over a wide area, except two end sections in an axial direction, at the outer peripheral surface 44 of the mating section of the connector pin 43.
In the connector for electric connection shown in FIG. 10, because a contact terminal is inserted into a board and fixed therein by soldering, there is a not-insignificant risk of degrading assemblability. Furthermore, because the tubular body 41 is used, a diameter of the connector pin 43 increases and also connector pins 43 are difficult to arrange with a fine pitch (for example, at most 1.2 mm).
A pressure contact holding-type connector (Japanese Patent Application Laid-open No. 2002-158053), in which the connector pin for electric connection was improved is a pressure contact holding-type connector 54 comprising, as shown in FIG. 11, an insulating housing 48, a plurality of through-holes 49 provided in a thickness direction of the housing 48, nearly cap-like conductive toe-pins 50 slidably fitted from one surface side of the housing 48 into each through-hole 49, conductive pins 51 slidably fitted from another surface side of the housing 48 into the through-holes 49 and also fitted into the conductive toe-pins 50, and springs 53 fitted into each through-hole 49, brought into contact with open end sections 52 of the conductive toe-pins 50, and passing through to the conductive pins 51, wherein the conductive toe-pins 50 and conductive pins 51 are caused to protrude from the housing 48 by a thrusting force of the spring 53.
This pressure contact holding-type connector shown in FIG. 11 can be mounted onto an electronic circuit board itself. End portions of the conductive pins comprising pins using, for example, gold-plated conductive copper, brass, aluminum, or conductive elastomer, are formed to have a shape sharpened at a prescribed angle or a pointed shape of a cone, pyramid, or the like, so that they can break an oxide film present on solder of electrodes that are to be connected, thereby enabling good conduction. Furthermore, because the conductive toe-pins 50 and conductive pins 51 are always in direct contact and form a shortest conduction path, a conduction path is reduced, inductance can be greatly decreased, and a high frequency characteristic can be realized. In addition, an entire length of the conductive pins 51 can be reduced. However, because the conductive toe-pins 50 and conductive pins 51 are in sliding contact on peripheral surfaces thereof, a pressure force necessary to provide for conduction between electrodes increases. Furthermore, because the conductive pins 51 pass through inside a coil of the spring 53 in a locked state, a stroke of the conductive pins tends to be relatively small by comparison with an entire length of the spring.
In a modification-example of the pressure contact holding-type connector of this type (Japanese Patent Application Laid-open No. 2002-158053), which is not shown in the figures, a conductive pin is provided with a flange section, which is engaged with a small-diameter section of a housing to prevent the conductive pin from slipping out of the housing.
A pressure contact holding-type connector of another type in which the connector pin for electric connection was improved (Japanese Patent Application Laid-open No. 2002-100431) is a pressure contact holding-type connector 55 that is to be interposed and held between opposing electrodes, wherein conductive spring elements 60 formed to have a nearly conical shape are fitted into through-holes 56 of an insulating housing 57 having a plurality of through-holes 56 oriented in a thickness direction. A diameter of at least one end portion of a spring element is formed larger than a diameter of other end portions, a cap 58 is mounted on a large-diameter end portion, a plug 59 is mounted on a distal end, and the spring element is provided so as to protrude from a surface of the housing 57 at a side of the other end portions. Electric conduction is ensured from the plug 59, that is in contact with one electrode, to the cap, that is in contact with another electrode, via spring element 60 that has good conductivity.
In the pressure contact holding-type connector of this type, a length of the plug 59 can be decreased by mating an end portion of the spring element 60 with a toric neck section provided in the plug 59, and almost an entire length of the spring element 60 can serve as a stroke for the plug 59. Another specific feature is because the connector has no sliding contact sections with surface contact, a pushing force necessary to move the plug 59 back and forth can be reduced.
However, in the pressure contact holding-type connector of this type, because a rather large portion of the spring element 60 protrudes from the housing 57, this extending portion can be extended or deformed by an inadvertently applied external force during mounting, transportation or maintenance, or the plug 59 fitted into the spring element 60 can separate from the spring element 60.